How Cold Rolling Changes Titanium Plate
Hot rolling breaks a titanium ingot or slab down to plate and coil, but it is cold rolling that fixes the final thickness, flatness and surface quality. Cold rolling is performed below the recrystallisation temperature of the alloy, so the metal work-hardens instead of softening as it passes through the rolls. Every pass raises dislocation density, which increases yield strength and hardness while reducing ductility. This is why a cold-rolled titanium plate is stronger than the same grade in the hot-rolled and annealed condition, and why the rolling schedule is built around pass count, reduction per pass and the inter-pass annealing steps.
For commercially pure (CP) titanium, recrystallisation begins in the region of 550-700 °C depending on the interstitial oxygen level, so the strip entering the rolls is kept well below that window. Grades with higher oxygen and iron content, such as ASTM B265 Grade 4, work-harden faster than soft Grade 1 and need more frequent intermediate annealing. Ti-6Al-4V (Grade 5) is even more sensitive, so a two-stage schedule with vacuum or inert-gas annealing between stages is normal mill practice.
The practical benefit is control. A cold-rolled plate can be delivered in the soft annealed condition, in a quarter-hard or half-hard condition produced by controlled cold reduction, or in a stress-relieved state where dimensional stability matters more than peak ductility. Buyers should state the required temper, because the same grade at the same thickness behaves very differently depending on how much cold work remains in the finished plate.
Cold-Rolled Grades and Typical Mechanical Properties
Plate, sheet and strip produced to ASTM B265 / B265M is the usual reference specification for wrought titanium, while GB/T 3621 covers titanium and titanium alloy plate for the Chinese market and ASTM F67 applies to unalloyed titanium for surgical implants. The table below lists annealed minimum values commonly quoted for plate product forms; actual results are reported heat by heat on the mill certificate.
| Grade | Nominal composition | Tensile strength, min | Yield strength, min | Elongation, min |
|---|---|---|---|---|
| Grade 1 | CP titanium, low oxygen | 240 MPa | 138 MPa | 24 % |
| Grade 2 | CP titanium, standard oxygen | 345 MPa | 275 MPa | 20 % |
| Grade 4 | CP titanium, higher oxygen and iron | 550 MPa | 483 MPa | 15 % |
| Grade 5 | Ti-6Al-4V | 895 MPa | 828 MPa | 10 % |
| Grade 7 | CP titanium with palladium addition | 345 MPa | 275 MPa | 20 % |
Density of titanium is about 4.51 g/cm³, roughly 57 % of steel, which makes the plate attractive wherever moving mass must be reduced.
Melting point is approximately 1668 °C and the elastic modulus of CP grades is in the 105-120 GPa range.
Palladium-bearing grades such as Grade 7 and Grade 11 are selected for mildly reducing acid service; Grades 26 and 27 use ruthenium instead of palladium for similar corrosion resistance at lower cost.
Ti-6Al-4V plate is the aerospace workhorse and is also standard for pressure vessels, subsea hardware and medical components where the strength-to-weight ratio is the deciding factor.
Mill Practice: Reduction, Annealing and Straightening
A typical cold-rolling route starts with hot-rolled and pickled coil, which is descaled mechanically or by acid pickling before the first cold pass. Total cold reduction is broken into several passes with intermediate anneals, and the annealing step is carried out in a vacuum furnace or under a protective atmosphere so that the oxygen and nitrogen pickup stays inside specification. After the final pass, plate is annealed or stress relieved, then roller-levelled and, where required, cut to length.
Two points decide the final quality. First, roll condition and lubrication control the surface; a worn or poorly cooled roll leaves transfer marks, chatter and a dull finish that no later operation removes. Second, levelness control after annealing prevents the bow and twist that appear when residual stress is released during laser cutting or machining at the customer's works. A supplier who reports flatness in millimetres per metre, not merely "flat", is easier to qualify.
Sizes, Tolerances and Surface Finish
Cold-rolled titanium plate is commonly supplied in thicknesses from a fraction of a millimetre up to a few millimetres of finished gauge, with wider gauges supplied as hot-rolled plate. Thickness tolerance, width, length, edge condition and flatness are all specified in the purchase order, and the commercial grades of finish are normally described as mill finish, pickled, bright annealed or ground.
Thickness tolerance is quoted as a plus/minus band, and the tightest classes cost more because they require extra passes and more frequent gauge checks.
Length and width tolerances are quoted separately from thickness tolerance; sheared edges are standard and machined edges suit subsequent welding or seal applications.
Surface condition should be agreed before rolling, because pickling removes the oxide layer but slightly changes the final thickness and roughness.
Coil, cut-to-length plate and sheared sheet are all normal delivery forms, and each form has its own packaging and handling requirement.
Where Cold-Rolled Titanium Plate Is Used
Chemical process equipment uses cold-rolled titanium for heat exchanger shells, tube sheets, reaction vessels and piping where chlorides would destroy stainless steel. Desalination plants use it for tubing and plate in the high-temperature brine sections. Aerospace and defence programmes use Ti-6Al-4V plate for structural brackets, frames and fittings where every kilogram counts. Medical device makers use unalloyed grades such as Grade 2 and Grade 4 for implant plates and housings, and automotive and motorsport engineering uses cold-rolled titanium for exhaust components, fasteners and lightweight body panels.
In each case the specification package should list the grade, the applicable standard, the temper, the mechanical test requirements, the surface finish and the packaging method, so that the plate arriving at the works is ready for the next operation rather than needing rework.
FAQ: Cold-Rolled Titanium Plate
Q: Why is cold-rolled titanium stronger than hot-rolled titanium of the same grade?
Cold rolling is carried out below the recrystallisation temperature, so the metal work-hardens and retains a high dislocation density instead of recovering its soft annealed structure.
Q: Can a cold-rolled plate be delivered in a fully soft condition?
Yes. After the final rolling pass the plate is annealed at a temperature above recrystallisation under vacuum or protective atmosphere to restore ductility and relieve rolling stress.
Q: Which standard should be called out on the purchase order?
ASTM B265 / B265M is the usual choice for wrought titanium plate and sheet, GB/T 3621 covers titanium plate in the Chinese market, and ASTM F67 applies to unalloyed titanium for surgical implants.
Q: What is the practical difference between Grade 2 and Grade 5 plate?
Grade 2 is commercially pure titanium with excellent formability and corrosion resistance, while Grade 5 is Ti-6Al-4V with roughly double the strength for structural and aerospace duty.
Q: How should cold-rolled titanium plate be stored?
Keep it dry, off the floor and separated from carbon steel to avoid iron contamination and galvanic staining; protective film or interleaving paper prevents surface scratching during transport.
Q: Does cold rolling affect corrosion resistance?
The annealed surface has the same corrosion resistance as hot-rolled material of the same grade, but heavy cold work without annealing can leave residual stress that promotes cracking in some service environments.